A. Field of the Invention
The present invention relates to methods and apparatus for grinding the front cutting portion or tip of twist drill bits. More particularly, the invention relates to an apparatus and method for automatically grinding or re-pointing twist drill bits that includes automatic means for removing dirt from the drill bit.
B. Description of Background Art
Printed wiring boards (PWB""s) used to hold and electrically interconnect electronic circuit components are typically fabricated as laminated stacks of copper foil sheets alternating with insulating sheets made of fiberglass, the latter containing glass fibers imbedded within a solidified resin such as epoxy. Glass fibers are highly abrasive, and can quickly dull drill bits used to drill holes in a PWB for receiving component leads, or for forming passageways or vias through the PWB. A typical PWB has a thickness of about 0.062 inch, and has hundreds of holes drilled through it. Each contact with the upper surface of a PWB to drill a hole is referred to as a xe2x80x9chit.xe2x80x9d Since PWB""s are usually arranged in stacks of two to five boards for drilling, a corresponding number of holes are drilled for each hit. Because the abrasive nature of the PWB board materials dulls typical drill bits after about 3000-5000 holes are drilled, drill bits used for such applications must be removed from service and re-sharpened after about 1,500-2,500 hits.
In conventional drill bit grinding apparatus used to sharpen or re-point twist drill bits, the drill bit must be held in a chuck while being re-pointed. Consequently, the operator must manually perform operations such as inserting the drill into the chuck of a drill bit holder mechanism, tightening the chuck to grip the drill, positioning or aligning the drill in relation to the drill bit holding mechanism and to rotary grinding stones, advancing the drill bit towards grindstones, retracting the re-pointed drill bit from the grindstones and removing the re-pointed drill bit. Because of all of the aforementioned operations, an operator can usually operate only a single drill bit grinding apparatus at a time. Thus, even an experienced operator can typically re-point no more than about 800 to 1,000 drill bits over an eight-hour work shift. Therefore, there has been a strong demand for an automated drill bit re-pointing apparatus that has a higher throughput rate than existing re-pointing apparatuses, and which may be operated by less than highly skilled personnel. Thus, for the small twist drill bits which are used to drill holes in printed wiring boards (PWB""s), equipment has been developed for re-pointing the front cutting portion of the bits including the tips, to thereby prolong the life span of bits which would otherwise have to be disposed of for not meeting dimensional tolerance requirements. Traditionally, the re-pointing process requires as an initial step removal of dirt which has inadvertently adhered to the drill bit. According to customary prior art methods, dirt is removed from a bit prior to re-pointing the bit by momentarily directing a blast of compressed air onto the surface of the bit. Next, the bit is installed in a clamping mechanism, and adjusted to a precisely pre-determined spatial position and angular orientation or phase angle of the flutes relative to abrasive grinding wheels. The grinding wheels are then brought into contact with the front cutting portion of the bit while the shank is rotated about the longitudinal axis of the bit to thereby vary the angular orientation or phase angle of the fluted portion of the bit presented to the grinding wheels. Upon completion of the grinding operation, the bit must be cleaned a second time, to remove particles of grindstone material, metal chips, or oil which may have adhered to the bit. A quality control inspection is then made of the bit to determine whether or not the bit meets pre-determined quality control criteria. Also, a ring-shaped collar is then customarily press-fitted onto the drill bit shank to identify the size of the bit and to limit its insertion depth into a workpiece.
Existing drill bit re-pointing apparatus functioning as described above experience certain problems which limit their effectiveness. For example, typical existing drill bit re-pointing methods utilize physically separated work stations to perform the various steps required in the re-pointing process. This arrangement has the disadvantage of requiring time and personnel to transport drill bits between the respective re-pointing stations, and of requiring a relatively large installation space for the various pieces of required equipment located at physically separated stations.
Moreover, in utilizing prior art methods for removing dirt from drill bits to prepare the bits for re-pointing, compressed air commonly used for dirt removal is problematic for several reasons. First, the small size of the bits and the preciseness of the re-pointing operation necessitates that the compressed air have a relative higher level of purity than normally required and supplied for typical factory production operations. Second, use of compressed air produces undesirable noise. Third, blasting dirt off a bit with compressed air causes the dirt to be scattered in an uncontrolled fashion to areas adjacent to the air gun.
In view of the problems mentioned above, the present invention was conceived to accomplish the following objectives.
An object of the present invention is to provide an automatic re-pointing apparatus and method for twist drill bits in which batches of drill bits may be re-pointed by a sequence of steps performed at a single location by an automatic re-pointing apparatus.
Another object of the invention is to provide apparatus and method for removing dirt from a drill bit to be re-pointed, by an automatic removal apparatus which does not require use of compressed air.
Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.
It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims.
Briefly stated, the present invention comprehends an apparatus for pointing twist drill bits, the apparatus including at least one and preferably two dirt removal mechanisms.
A drill bit pointing and dust removal apparatus according to the present invention includes a drill bit processing unit which has a rotary index plate on which are mounted a plurality of circumferentially spaced apart drill bit holder units. Spaced radially apart from the periphery of the index plate are a plurality of circumferentially spaced apart, fixed drill bit processing stations where separate processing units each perform a separate processing function on an individual drill bit which has been rotated by the index plate into position adjacent to a particular station. Spaced radially apart from the periphery of the rotary pedestal are a plurality of circumferentially spaced apart operation stations where separate operation units each perform a separate operation on an individual drill bit which has been rotated by the rotary pedestal into position adjacent to a particular operation station. The loading unit includes a loading unit which has a rotary pedestal on which are located a plurality of circumferentially spaced apart transfer arms, each adapted to hold a separate drill bit. The apparatus includes actuator mechanisms which transfer an individual bit from an arm on the loading unit rotary pedestal to an individual drill bit holder on the processing unit index plate at the beginning of a drill bit processing cycle, and from an individual drill bit holder to an arm on the loading unit base plate at the end of a process cycle. The loading unit rotary pedestal is then rotated to transfer a processed drill bit to a reject container station, ring adjustment station, and input/output station located in a circle around the periphery of the loading unit pedestal, to be scrapped if defective, or fitted with an identification ring and unloaded from the loading unit base plate into a transport container for transport away from the apparatus, e.g., to a shipping location.
The apparatus according to the present invention includes position control mechanisms which consist of operatively interactive sensors and actuators located at fixed processing stations and on each multi-purpose drill bit holder unit on the processing unit index plate. The position control mechanisms include a tip position adjustment mechanism which maintains the tip of a drill bit in a predetermined, fixed position, a center adjustment mechanism that positions the center of the drill bit core at a predetermined elevation, and a phase-adjustment mechanism which adjust the rotation angle or phase of the bit to predetermined values.
According to the invention, a drill bit to be subjected to re-pointing and/or other processes by the apparatus is first loaded onto an arm on the rotary pedestal of the loading unit at an input/output station. The rotary pedestal is then rotated to a pre-grind dirt removal operation station, where dirt is removed from the drill bit. Next, the rotary pedestal is rotated to a load/unload station adjacent to the processing unit, where the pre-cleaned bit is transferred to the index plate of the processing unit. According to the invention, an individual drill bit in a holder on the processing unit index plate successively encounters a series of drill bit processing stations located adjacent to the periphery of the processing unit index plate, including in order, an optical tip position set up sensing and alignment station for providing control signals which are used to adjust the position of the drill bit, a grinding station, a second, post-grind dirt removal station, and an optical inspection station.
A dirt removal apparatus for removing dirt from a drill bit tip according to the present invention includes a plastically deformable body which has a tacky surface, and an actuator mechanism for bringing the body into contact with a drill bit tip, whereupon dirt lightly adhered to the drill bit adheres more strongly to the tacky surface of the body, thus removing the dirt from the bit when the body is retracted from the bit. In a preferred embodiment, the dirt removal body has the form of a rotatable toroidal roller made of a synthetic polymer such as poly-isobutylene, that is easily deformable and has a tacky surface. The actuator mechanism pivots the toroidal roller into contact with a drill bit tip to clean the tip, and pivots the roller away from the tip, with dirt originally adhered to the drill bit surface now adhered to the roller. Pivotal motion of the dirt removal toroidal roller away from the tip causes the roller to rotate relative to silicone rubber dressing rollers which contact surfaces of the toroidal roller to thereby re-shape and re-surface the toroidal body, after it has been deformed and soiled in the process of cleaning a drill bit, thus preparing the toroidal roller to contact and clean a next drill bit.
Repointing of drill bits according to the method of the present invention includes the following steps. First, a drill bit is loaded onto one of the plurality of drill bit transfer arms mounted on the rotary pedestal of the loading unit which is adjacent to an input/output, or carry in/carry out station spaced radially outwards from the periphery of the loading unit base plate. The loading unit rotary pedestal is then rotated a predetermined angle to position the bit adjacent to a first, pre-grind dirt removal processing station, where the bit is cleaned: the loading unit rotary pedestal is then rotated a predetermined angle to a loading/unloading transfer station located between the loading unit and processing unit, where the cleaned bit is then loaded onto an empty drill bit holder on the processing unit index plate by actuation of the transfer arm holding the bit. The processing unit index plate is then rotated a first angular increment to locate the bit holder and bit adjacent to a tip position set up processing station where an electro-optical sensing apparatus views the bit and in response to that view, produces control signals which are applied to actuator mechanisms which adjust the position of the tip of the drill bit to a predetermined location in the field of view of the sensing apparatus, adjust the height of the center of the bit, and adjust the rotation angle or phase angle of the fluted portion of the tip to a predetermined angle relative to a reference plane. The index plate is once again incrementally rotated to position the drill bit holder and drill bit adjacent to a grinding wheel station which has a pair of rotating grindstones mounted on a traverse mechanism which translates the rotating grindstones forcibly against surfaces of a drill bit to thereby automatically grind the tip to a predetermined shape. The index plate is again rotatably incremented to position the drill bit holder and bit adjacent to a second, post-grind dirt removal station, where the bit is again cleaned. Next, the index plate is incrementally rotated to position the ground and cleaned re-pointed drill bit adjacent to an electro-optical inspection station, which uses a computer and pattern recognition logic to determine whether the re-pointed drill bit meets size and shape specifications. The index plate is once again rotated to position the drill bit holder holding the re-pointed, cleaned, and inspected drill bit back at the loading/unloading transfer station, adjacent to an empty transfer arm on the pedestal of the loading unit, whereupon the transfer arm is actuated to grasp and remove the processed bit. The loading unit rotary pedestal is then incrementally rotated to position the transfer arm holding the re-pointed bit adjacent to a reject container, at which location the arm is actuated to deposit a rejected bit into the reject container. The loading unit rotary pedestal is then incrementally rotated to position the transfer arm holding an acceptable re-pointed drill bit adjacent to a ring installation unit, where an identifying ring press-fitted onto the shank of the bit is adjusted to a proper distance from the drill bit tip. The loading unit rotary pedestal is then incrementally rotated to position the drill bit transfer arm holding a finished re-pointed bit adjacent to the input/output station, where the transfer arm transfers the bit to a transport container.
The processing unit index plate and loading unit pedestal have equal numbers, e.g., five, of drill bit holders and transfer arms, respectively, which are separated by the same central angles, e.g., 72 degrees. Also, the relative positions and movements of the drill bit holders and transfer arms, as well as functions of the processing and loading stations, are synchronized by a transport control unit, which comprises a microprocessor or general purpose computer such as a PC, which also synchronizes rotations of the processing unit index plate and the loading unit pedestal. Therefore, each of the foregoing operations described at the various stations adjacent to the processing unit and loading unit are performed simultaneously on five different drill bits, thus resulting in a high processing through-put rate.